Finishing the engine

Alright, it has been two months and I have been plugging away at the engine that whole time when I got a chance.  It was a long process that was really helped by a great step by step procedure someone in the UK had documented (link).

We left off after having redone the jugs and heads, after this it was on to the main case and separating and cleaning it up.

Undoing all of the very rusted case bolts, I had to smack it good a few times with a mallet to separate it.

Inside you can see the crank up front and the two transmission shafts in the back.  I pulled out my caliper and measured the crank play and everything was in spec.  I pulled everything from the two case halves and tagged and bagged it.  Now it was time to get down to cleaning the cases.

Now case cleaning was a pain...in...the...ass.  The top half was pretty straight forward, some degreaser and scotchbrite pads got me a pretty good looking result.  The bottom half was heavily oxidized and super dinged up.  The front portion of the lower half is covered in aluminum cooling fins and my grandfather really only rode his bike around on the dirt roads near our farm.  This means that rocks that were run over by the front tires were picked up and thrown at the underside of the engine.  I cleaned and cleaned with degreaser and scotchbrite, hit it with the soda blaster, and event resorted to using a small screwdriver and mineral spirits on a rag trying to scrape and dissolve the worst of it.  Here are my results, not concours quality, but pretty damn good.

So having gone through the struggle of cleaning up all of the parts it was time to start reassembly of the engine.  Through this process I learned pretty much how everything on the motorcycle worked including the gearbox, which was the most interesting part and where the rebuild begins.

First thing we do is install the selector drum and the selector forks.

Then we install the inter meshing transmission gears.

Now we install the crankshaft.  Throughout this process I am replacing all of the rubber seals in the engine.  With a two stroke engine the portion of the case around the crank must be air tight since the fuel oil mix move both above and below the pistons to assure the lubrication, if you have an air leak the fuel mix will lean out and then you will start melting holes in pistons or seize the engine.  This is why I tore apart a working engine, this way I know everything is up to spec.  The next step is applying special RTV sealant to the bottom half of the case everywhere it meets the top case and dropping the top half on the bottom half and tightening the bolts.

Tada!  Now I reinstalled the array of gears, the rebuilt clutch, and the rest of the inner workings that mount to each side of the sealed up case.  Then we get to add our shiny restored covers.

Then we install the cleaned up jugs and heads.

I need to hit the sides of those heads with some more aluminum polish and a buffing wheel, but lets remind ourselves how far we have come.

Now the last step is to make sure all of those new seals and the case sealer I used sealed up our crankcase.  Now they sell a special leak down tester for two stroke engines, it costs, wait for it, $250!  Now this tester just comes with two things to plug up the two exhaust ports and two other things that plug the intake and allows you to pump it up and measure the pressure.  I decided to do this for under $20, with some PVC ends that I RTV sealed a tire valve and a pressure gauge from a farm sprayer, to plug the exhaust I bought some freeze plugs from the auto parts store and I pressurized the engine with 5 psi from a bicycle pump.

I had some air leaks around the rubber intake boots (where it meets the reed cage), I applied some left over engine sealer from the cases and let it harden and the pressure gauge above shows my results.  A near perfect seal, I held 5 psi with almost no fluctuation for 6 minutes!

I did rebuild the clutch while I was at it and found the first thing that needed wear based replacment, clutch springs.  I will order a set with my next bulk order from Economy Cycle.  I did end up replacing the clutch friction discs since one was cracked when I opened it up (I might have broke it trying to get it out).

Next up will either be the front brake or the frame.